/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */
package org.apache.tomcat.util.file;

import org.apache.tomcat.util.res.StringManager;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;

/**
 * This class is used to obtain {@link InputStream}s for configuration files
 * from a given location String. This allows greater flexibility than these
 * files having to be loaded directly from a file system.
 */
public class ConfigFileLoader {

	private static final StringManager sm = StringManager.getManager(ConfigFileLoader.class
			.getPackage().getName());

	private static final File CATALINA_BASE_FILE;
	private static final URI CATALINA_BASE_URI;

	static {
		String catalinaBase = System.getProperty("catalina.base");
		if (catalinaBase != null) {
			CATALINA_BASE_FILE = new File(catalinaBase);
			CATALINA_BASE_URI = CATALINA_BASE_FILE.toURI();
		} else {
			CATALINA_BASE_FILE = null;
			CATALINA_BASE_URI = null;
		}
	}

	private ConfigFileLoader() {
		// Utility class. Hide the default constructor.
	}

	/**
	 * Load the resource from the specified location.
	 *
	 * @param location The location for the resource of interest. The location
	 *                 may be a URL or a file path. Relative paths will be
	 *                 resolved against CATALINA_BASE.
	 * @return The InputStream for the given resource. The caller is responsible
	 * for closing this stream when it is no longer used.
	 * @throws IOException If an InputStream cannot be created using the
	 *                     provided location
	 */
	public static InputStream getInputStream(String location) throws IOException {
		// Absolute URIs will be left alone
		// Relative files will be resolved relative to catalina base
		// Absolute files will be converted to URIs

		// Location was originally always a file before URI support was added so
		// try file first.

		// First guess, an absolute file path
		File file = new File(location);

		if (!file.isAbsolute()) {
			// Second guess, a file path relative to CATALINA_BASE
			file = new File(CATALINA_BASE_FILE, location);
		}

		if (file.isFile()) {
			return new FileInputStream(file);
		}

		// Third and final guess, a URI
		URI uri;
		if (CATALINA_BASE_URI != null) {
			uri = CATALINA_BASE_URI.resolve(location);
		} else {
			uri = URI.create(location);
		}

		// Obtain the input stream we need
		try {
			return uri.toURL().openStream();
		} catch (IllegalArgumentException e) {
			throw new IOException(sm.getString("configFileLoader.cannotObtainURL", location), e);
		}
	}
}
